Various types of hammer actuator systems for use in dot matrix and other types of printers have been proposed and are in use. In most print hammer actuators systems, hammer actuation is controlled by controlling the current flow through coils. The coils produce magnetic fields that interact with the hammers (which may comprise several elements at least one of which is formed of a ferromagnetic material) so as to pull the hammers against a spring force and then release the electromagnetic pulling force whereby the stored spring force creates hammer actuation. Hammer actuation creates a character or a portion thereof (e.g., a dot) on a suitable print receiving medium.
One type of printer wherein such hammer actuator systems have found widespread use is the dot matrix line printer. Dot matrix line printers are produced by the Tally Corporation, Kent, Wash.; and, an example of a dot matrix line printer is described in U.S. Pat. No. 3,782,278, entitled IMPACT LINE PRINTER by David L. Barnett et al., assigned to the Tally Corporation. In a dot matrix line printer, a plurality of print hammers are oscillated (moved back and forth) between a print receiving medium (e.g., paper) and a line of actuating coils. In the past, in dot matrix line printers of the type described in the foregoing patent, each hammer has been associated with a single coil. The coils have been mounted in a fixed position and the related hammer has remained in the narrow region where the coils' magnetic field strength is adequate to actuate the related hammer. More specifically, as the hammers are oscillated the coils are selectively energized to pull the hammers away from the print receiving medium and, thereby, stress the hammer springs. The hammers are then released, whereby dots are created on the print receiving medium. After each dot line is completed, the paper is incremented and the hammers are oscillated in the opposite direction during which time a second line of dots is created in predetermined positions. A series of dot lines creates a line of characters. The characters may be formed by 5.times.7 or 7.times.9 dot matrix arrays, for examples.
While, in the past, in general, a single coil has been dedicated to a single hammer in dot matrix line printers, a recently issued patent (U.S. Pat. No. 4,080,892), entitled APPARATUS FOR DRIVING DOTTING HAMMERS OF A MATRIX PRINTER by Issei Imahashi (U.S. Pat. No. 4,080,892), has suggested using either of two coils to actuate a single dot printing element. More specifically, in this printing arrangement the coils are mounted in a fixed position on one side of the print receiving medium. The dot printing elements are located on the other side of the print receiving medium and movable back-and-forth in the magnetic fields produced by energized coils. Two coils are associated with each hammer and either (but not both) of the coils can be used to pull the hammer toward the print receiving medium to create a dot. Which coil is chosen to be energized, of course, depends upon the position of the hammer when a dot is to be printed. In other words, the pitch or spacing arrangement of the parallel electromagnets is preferably half of the pitch arrangement of the electromagnetic plates to be attracted.
In prior art dot matrix line printers that have had a one-to-one coil/hammer relationship character width has been very limited when the coils are mounted in a fixed position and the hammers are oscillated. This limitation exists because, when the hammers are moved very far from the coils, the attraction force for a fixed amount of energization rapidly drops whereby the printed dots become lighter. This limitation has restricted such printers to the printing of relatively narrow characters, such as the English language characters. It has been difficult, and in many cases impossible, to print wider characters (such as those common to Asian and African languages) of uniform intensity dots, without making the resulting printer overly complex and, therefore, undesirably expensive. For example, while the amount of power applied to the coils could be made to depend upon hammer position, such an approach requires an expensive electronic control system having undesirable time delays. Moreover, the size of the required power supply would have to be relatively large, whereby additional cooling would be required, both of which would increase the costs of such a printer. Printers using coil/hammer relationships where multiple coils can act one-at-a-time on a single hammer have similar disadvantages. For example, relatively light dots are created in the space between coils, whereby such systems create difficult to read characters even though they have the inherent ability to create relatively wide characters. Moreover, prior art dot matrix line printers have been difficult to use to create graphs, drawings and the like, all of which require that a dot printer have the ability to create a continuous line of similar intensity dot across substantially an entire page of the print receiving medium.
While the present invention was developed for use in connection with dot matrix line printers of the types briefly described above, it should be understood that the invention can also be used with other types of mechanical mechanisms to control the actuation of hammer-type elements.
It is an object of this invention to provide a new and improved hammer actuator system.
It is a further object of this invention to provide a print hammer actuator system wherein the magnetic fields produced by adjacent coils cooperate to actuate the print hammers.
It is another object of this invention to provide a dot matrix line printer hammer actuator system wherein the magnetic fields produced by two adjacent coils cooperate to actuate a single print hammer.
It is a still further object of this invention to provide a new and improved dot matrix line printer having the capability of producing dots of substantially the same intensity at substantially any horizontal position across a print receiving medium.